Although a smartphone, a key, a wallet, and a handbag are a device and items that are necessary to be kept when going out, they are very vulnerable items that can be lost. If these items are lost, then it will result in a significant loss of economy and time as well as a psychological damage for their owner. Particularly, the inner contents of the smartphone contain all personal information such as phone numbers, schedules, and other privately sensitive things as well as a certificate for financial transactions and credit card information. Even worse, it will significantly influence material loss and psychological impact, which is incomparable to the loss of a traditional wallet or a credit card. Furthermore, the current smartphone unlike an old phone in the past is such a valuable and expensive thing such that it costs around $1,000, and if it is found by someone, then it may be possible to sell it to other people and it will rarely return to the smartphone owner. Therefore, the lost mobile phone is not returned to the owner.
At present, Apple and Google as a manufacturer of a mobile phone's operating systems like iOS and Android provide a kill switch program like “Find My iPhone” service by Apple, Inc. and “Device Manager” by Google, Inc., and in case of loss and theft of a phone, a phone owner has to use another phone or a computer to display the location on the map in order to track the phone that is expected to be lost or stolen. In addition, it can attempt to find the phone by generating maximal alerting sound, and it can remotely erase all the content of the phone which may be lost or stolen when it is determined not to obtain the phone in the worst case. But this technology cannot properly support necessary measures even at the just instant when the phone is actually lost or stolen. When an owner of the lost phone cannot access his own phone at that moment, he has to find and access his own computer or borrow his neighbor's phone at that time. Due to a delay of an initial reaction, only this technology gives a lack of usefulness and inconveniences for providing proper measures. And in the case of Apple, Inc., an anti-loss method of an Apple watch and a wireless earphone called AirPods which is connected to a smartphone both work in the same manner like a smartphone. This anti-loss method is possible to be only applicable when the corresponding device and the smartphone are located within a mutual communication range, and it is difficult to even apply for the case when it is out of range.
Furthermore, except in the case of a wearable device like a watch, when portable items such as a wallet, a key, and other valuable things that are possessed by a smartphone's owner are lost or stolen, a method which can extend to a search space and an operating time to find the lost and stolen thing by mutual monitoring based on cooperation between a smartphone and portable things has not been raised yet.